java - 抽象类及其子类

Question

我有以下代码是我在网上找到的，这可能是一个简单的问题，但你的解释对我有很大帮助。

这是名为 SongComponent 的抽象类

public abstract class SongComponent {

    public void add(SongComponent newSongComponent){

        throw new UnsupportedOperationException();

    }
    public void remove(SongComponent newSongComponent){

        throw new UnsupportedOperationException();

    }

    public SongComponent getComponent(int componentIndex){

        throw new UnsupportedOperationException();

    }

    public String getSongName(){

        throw new UnsupportedOperationException();

    }

    public String getBandName(){

        throw new UnsupportedOperationException();

    }

    public int getReleaseYear(){

        throw new UnsupportedOperationException();

    }

    public void displaySongInfo(){

        throw new UnsupportedOperationException();

    }




}

这是扩展名为 SongGroup 的抽象类的类

import java.util.ArrayList;
import java.util.Iterator;
public class SongGroup extends SongComponent {

    ArrayList songComponents = new ArrayList();

    String groupName;
    String groupDescription;

    public SongGroup(String newGroupName, String newGroupDesc){

        groupName = newGroupName;
        groupDescription = newGroupDesc;


    }

    public String getGroupName(){
        return groupName;
    }

    public String getGroupDescription(){
        return groupDescription;
    }

    // It overrides the add() method from its superclass 
    public void add(SongComponent newSongComp){
        songComponents.add(newSongComp);
    }

    public void remove(SongComponent newSongComp){
        songComponents.remove(newSongComp);
    }

    public SongComponent getComponent(int compIndex){
        return (SongComponent)songComponents.get(compIndex);
    }

    public void displaySongInfo(){

        System.out.println( getGroupName() + " " + 
        getGroupDescription());

        Iterator songIterator = songComponents.iterator();

        while(songIterator.hasNext()){
            SongComponent songInfo = (SongComponent)songIterator.next();
            songInfo.displaySongInfo();
        }
    }


}

我的问题是，在什么情况下，add()方法和其他被抽象类重写的方法会被调用？比如抽象类的add()方法会抛出new UnsupportedOperationException异常，什么时候调用？

Answer 1

SongComponent可能有其他不覆盖 SongGroup 的具体子类(add() 除外) .对于此类子类，调用 add()将执行基类实现并抛出 UnsupportedOperationException异常。

SongComponent 的另一种实现方式将是使当前抛出的所有方法 UnsupportedOperationException抽象，这将强制 SongComponent 的任何具体子类覆盖它们。